In recent years much attention has been directed toward the development of new sources of protein for human consumption. There exists a need for protein material which can be incorporated in foods or which is usable as a basic proteinaceous substance for human consumption.
One possible solution to the problem of supplying the ever increasing world-wide need for food protein is provided by processes for the bio-synthetic manufacture of protein through the growth of microorganisms on various substrates. It is known, for example, that microorganisms such as bacteria and yeast, which are grown by single-cell reproduction, contain high proportions of proteins and can be treated to recover protein isolate.
In order for single-cell proteins to compete with vegetable proteins and to share the protein market, it is necessary that it be processed to remove nucleic acid, primarily ribonucleic acid (RNA).
The human metabolic system produces uric acid as the result of the metabolism of materials such as ribonucleic acid. Since man does not have a uricase enzyme system, uric acid is not broken down and excreted with urine. However, if produced in larger quantities than the body can excrete, the body stores uric acid leading to the condition known as gout.
In 1972, the Recommended Daily Allowance of The Food and Nutrition Board, National Research Counsel in protein was 65 grams per day for a 70 kilogram adult male. The Protein Advisory Group of the United Nations System recommended that the amount of nucleic acid ingested per day from microbial protein should be less than 2 grams. Therefore, the nucleic acid content of the protein should be less than 6%, if microbial protein supplied 50% of dietary protein. The nucleic acid content should be below about 3%, if microbial protein is the sole source of protein in the diet.
U.S. Pat. No. 4,168,262, to Kinsella et al., displays a process for reducing nucleic acid in microbial derived protein. This process is accomplished by disrupting microbial protein containing cells and then derivatizing the resultant mixture comprising protein, cell debris and nucleic acid with an acid anhydride, and then isoelectrically precipitating a nucleic acid diminished protein containing fraction, from a nucleic acid enriched supernatant. The protein product of this process is obtained as a derivatized protein such as citraconylated protein.